e*thirteen's cassette is no longer just a prototype and is moving into production. The cassette offers a very wide range with a 9-44 tooth spread on their 11-speed cassette, and a 9-42 tooth on the 10-speed version.
Due to the low 9-tooth count they had to get clever with the design. The multiple piece cassette includes two assemblies. The back assembly is machined from aluminum and includes either three or two gears depending on which speed setup you're using. This locks onto a SRAM XD driver body.
The remaining eight gears lock on using a chain whip. The front cluster is the same between both the 10- and 11-speed cassettes though the back cluster changes. e*thirteen uses a smaller cluster made from heat treated steel which is then machined to achieve the lightest weight possible. The use of steel improves longevity and durability. e*thirteen will sell this for $300 US, saving you quite a few $$$ over the leading competitor.
2016 Mountain Bike Components at Eurobike